Ultra-deep pyrosequencing detects conserved genomic sites and quantifies linkage of drug-resistant amino acid changes in the hepatitis B virus genome

Next-generation sequencing for the diagnosis of hepatitis B: current status and future prospects

INTRODUCTION

Hepatitis B virus (HBV) causes a complex and persistent infection with a major impact on patients health. Viral-genome sequencing can provide valuable information for characterizing virus genotype, infection dynamics and drug and vaccine resistance.

AREAS COVERED

This article reviews the current literature to describe the next-generation sequencing progress that facilitated a more comprehensive study of HBV quasispecies in diagnosis and clinical monitoring.

EXPERT OPINION

HBV variability plays a key role in liver disease progression and treatment efficacy. Second-generation sequencing improved the sensitivity for detecting and quantifying mutations, mixed genotypes and viral recombination. Third-generation sequencing enables the analysis of the entire HBV genome, although the high error rate limits its use in clinical practice.

Intra-host diversity of hepatitis B virus during mother-to-child transmission: the X gene may play a key role in virus survival in children after transmission

Mother-to-child transmission of hepatitis B virus (HBV) is the main route of transmission in Asia, and characterization of HBV quasispecies is needed to further understand virus evolution and adaptation. To understand changes in HBV during mother-to-child transmission, we enrolled nine pairs of mothers and children in the study, including a set of twins. Three groups were infected with HBV genotype C, and six groups were infected with HBV genotype B. The full-length HBV genome was amplified by PCR from serum samples before antiviral treatment, the whole viral genomes from each pair were sequenced, and the complexity and diversity of the quasispecies were analyzed. The entropy of transmitted HBV in children was found to be lower than their mothers, suggesting that there was a bottleneck effect during HBV transmission from the mother to the child. Selective evolution was shown by calculating πN and πS in the whole genomes, and the highest values were obtained for the X gene, which plays a role in viral replication and immune escape. All genotype C patients and only one genotype B pair had a πN/πS greater than 1 ratio, indicating that positive selection had occurred. In addition, quasispecies were found to be different between the twin children despite having the same mother, indicating that virus evolution is host-specific.

Interaction of virus populations with their hosts

Viral population numbers are extremely large compared with those of their host species. Population bottlenecks are frequent during the life cycle of viruses and can reduce viral populations transiently to very few individuals. Viruses have to confront several types of constraints that can be divided into basal, cell-dependent, and organism-dependent constraints. Viruses overcome them exploiting a number of molecular mechanisms, with an important contribution of population numbers and genome variation. The adaptive potential of viruses is reflected in modifications of cell tropism and host range, escape to components of the host immune response, and capacity to alternate among different host species, among other phenotypic changes. Despite a fitness cost of most mutations required to overcome a selective constraint, viruses can find evolutionary pathways that ensure their survival in equilibrium with their hosts.

Machine-learning based patient classification using Hepatitis B virus full-length genome quasispecies from Asian and European cohorts

Chronic infection with Hepatitis B virus (HBV) is a major risk factor for the development of advanced liver disease including fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). The relative contribution of virological factors to disease progression has not been fully defined and tools aiding the deconvolution of complex patient virus profiles is an unmet clinical need. Variable viral mutant signatures develop within individual patients due to the low-fidelity replication of the viral polymerase creating 'quasispecies' populations. Here we present the first comprehensive survey of the diversity of HBV quasispecies through ultra-deep sequencing of the complete HBV genome across two distinct European and Asian patient populations. Seroconversion to the HBV e antigen (HBeAg) represents a critical clinical waymark in infected individuals. Using a machine learning approach, a model was developed to determine the viral variants that accurately classify HBeAg status. Serial surveys of patient quasispecies populations and advanced analytics will facilitate clinical decision support for chronic HBV infection and direct therapeutic strategies through improved patient stratification.

Insights From Deep Sequencing of the HBV Genome-Unique, Tiny, and Misunderstood

Hepatitis B virus (HBV) is a unique, tiny, partially double-stranded, reverse-transcribing DNA virus with proteins encoded by multiple overlapping reading frames. The substitution rate is surprisingly high for a DNA virus, but lower than that of other reverse transcribing organisms. More than 260 million people worldwide have chronic HBV infection, which causes 0.8 million deaths a year. Because of the high burden of disease, international health agencies have set the goal of eliminating HBV infection by 2030. Nonetheless, the intriguing HBV genome has not been well characterized. We summarize data on the HBV genome structure and replication cycle, explain and quantify diversity within and among infected individuals, and discuss advances that can be offered by application of next-generation sequencing technology. In-depth HBV genome analyses could increase our understanding of disease pathogenesis and allow us to better predict patient outcomes, optimize treatment, and develop new therapeutics.

Quantitative characterization of hepatitis delta virus genome edition by next-generation sequencing

AIM

To determine the capacity of next-generation sequencing (NGS) for quantifying edited and unedited HDV populations, and to confirm if edition is a general phenomenon taking place along the entire HDV region analyzed, as we previously reported (Homs M et al. PLoS One 2016, 11, e0158557).

METHODS

Four serum samples from 4 patients with chronic HDV/HBV infection were included in the study. The region selected for analysis covered 360 nucleotides (nt), positions 910-1270 of the HDV genome, which included the HDAg ORF editing site (nt 1014 within codon 196). Quantification of edited and unedited genomes was performed by molecular cloning and Sanger sequencing and by NGS. To evaluate the reliability of the NGS values obtained, we combined a clone with an edited codon and one with an unedited codon in known percentages in a series of artificial mixtures, which were then analyzed by NGS. In addition, we determined the nt changes occurring over the complete amplified region after excluding the editing codon (196) to evaluate edition along it.

RESULTS

In total, 11,208 quality-filtered sequences were obtained in the 4 samples. The 95% confidence intervals for the proportions of unedited populations by molecular cloning and NGS were overlapping, and those of cloning were wider, indicating that they are comparable and that NGS is more precise than cloning. Unedited genomes predominated over edited ones in all 4 samples analyzed by NGS and in 3 of the 4 samples analyzed by molecular cloning. In total, 83,276 quality-filtered sequences were obtained from the artificial mixtures. Percentages of the two viral populations detected by NGS in these mixtures were comparable to the expected percentages. Evaluation of edition along the HDV coding region showed that transitions were more frequent than transversions, accounting for 63.09% and 36.91%, respectively. Interestingly, among the 4 possible transition-type changes, G:A and A:G accounted for 73.86% of the total.

CONCLUSION

Next-generation sequencing proved useful to quantify edited and unedited HDV genomes, and provided relevant information on the HDV quasispecies.

How viral genetic variants and genotypes influence disease and treatment outcome of chronic hepatitis B. Time for an individualised approach?

Chronic hepatitis B virus (HBV) infection remains a global problem. Several HBV genotypes exist with different biology and geographical prevalence. Whilst the future aim of HBV treatment remains viral eradication, current treatment strategies aim to suppress the virus and prevent the progression of liver disease. Current strategies also involve identification of patients for treatment, namely those at risk of progressive liver disease. Identification of HBV genotype, HBV mutants and other predictive factors allow for tailoured treatments, and risk-surveillance pathways, such as hepatocellular cancer screening. In the future, these factors may enable stratification not only of treatment decisions, but also of patients at risk of higher relapse rates when current therapies are discontinued. Newer technologies, such as next-generation sequencing, to assess drug-resistant or immune escape variants and quasi-species heterogeneity in patients, may allow for more information-based treatment decisions between the clinician and the patient. This article serves to discuss how HBV genotypes and genetic variants impact not only upon the disease course and outcomes, but also current treatment strategies. Adopting a personalised genotypic approach may play a role in future strategies to combat the disease. Herein, we discuss new technologies that may allow more informed decision-making for response guided therapy in the battle against HBV.

Deep sequencing in the management of hepatitis virus infections

The hepatitis viruses represent a major public health problem worldwide. Procedures for characterization of the genomic composition of their populations, accurate diagnosis, identification of multiple infections, and information on inhibitor-escape mutants for treatment decisions are needed. Deep sequencing methodologies are extremely useful for these viruses since they replicate as complex and dynamic quasispecies swarms whose complexity and mutant composition are biologically relevant traits. Population complexity is a major challenge for disease prevention and control, but also an opportunity to distinguish among related but phenotypically distinct variants that might anticipate disease progression and treatment outcome. Detailed characterization of mutant spectra should permit choosing better treatment options, given the increasing number of new antiviral inhibitors available. In the present review we briefly summarize our experience on the use of deep sequencing for the management of hepatitis virus infections, particularly for hepatitis B and C viruses, and outline some possible new applications of deep sequencing for these important human pathogens.

Ultra-deep sequencing reveals high prevalence and broad structural diversity of hepatitis B surface antigen mutations in a global population

The diversity of the hepatitis B surface antigen (HBsAg) has a significant impact on the performance of diagnostic screening tests and the clinical outcome of hepatitis B infection. Neutralizing or diagnostic antibodies against the HBsAg are directed towards its highly conserved major hydrophilic region (MHR), in particular towards its “a” determinant subdomain. Here, we explored, on a global scale, the genetic diversity of the HBsAg MHR in a large, multi-ethnic cohort of randomly selected subjects with HBV infection from four continents. A total of 1553 HBsAg positive blood samples of subjects originating from 20 different countries across Africa, America, Asia and central Europe were characterized for amino acid variation in the MHR. Using highly sensitive ultra-deep sequencing, we found 72.8% of the successfully sequenced subjects (n = 1391) demonstrated amino acid sequence variation in the HBsAg MHR. This indicates that the global variation frequency in the HBsAg MHR is threefold higher than previously reported. The majority of the amino acid mutations were found in the HBV genotypes B (28.9%) and C (25.4%). Collectively, we identified 345 distinct amino acid mutations in the MHR. Among these, we report 62 previously unknown mutations, which extends the worldwide pool of currently known HBsAg MHR mutations by 22%. Importantly, topological analysis identified the “a” determinant upstream flanking region as the structurally most diverse subdomain of the HBsAg MHR. The highest prevalence of “a” determinant region mutations was observed in subjects from Asia, followed by the African, American and European cohorts, respectively. Finally, we found that more than half (59.3%) of all HBV subjects investigated carried multiple MHR mutations. Together, this worldwide ultra-deep sequencing based genotyping study reveals that the global prevalence and structural complexity of variation in the hepatitis B surface antigen have, to date, been significantly underappreciated.

HBV quasispecies composition in Lamivudine-failed chronic hepatitis B patients and its influence on virological response to Tenofovir-based rescue therapy

The present study sought to evaluate the structure of HBV quasispecies in Lamivudine (LMV)-failed chronic hepatitis B (CHB) patients and its impact in defining the subsequent virological responses to Tenofovir (TDF)-based rescue-therapy. By analyzing HBV clones encompassing reverse transcriptase (RT) and surface (S) region from LMV-failed and treatment-naïve CHB patients, we identified 5 classical and 12 novel substitutions in HBV/RT and 9 substitutions in immune-epitopes of HBV/S that were significantly associated with LMV failure. In silico analysis showed spatial proximity of some of the newly-identified, mutated RT residues to the RT catalytic centre while most S-substitutions caused alteration in epitope hydrophobicity. TDF administration resulted in virological response in 60% of LMV-failed patients at 24-week but non-response in 40% of patients even after 48-weeks. Significantly high frequencies of 6 S-substitutions and one novel RT-substitution, rtH124N with 6.5-fold-reduced susceptibility to TDF in vitro, were noted at baseline in TDF non-responders than responders. Follow-up studies depicted greater evolutionary drift of HBV quasispecies and significant decline in frequencies of 3 RT and 6 S-substitutions in responder-subgroup after 24-week TDF-therapy while most variants persisted in non-responders. Thus, we identified the HBV-RT/S variants that could potentially predict unfavorable response to LMV/TDF-therapy and impede immune-mediated viral clearance.

Deep Sequencing of the Hepatitis B Virus Genome: Analysis of Multiple Samples by Implementation of the Illumina Platform

The quasispecies variation of hepatitis B virus (HBV) was believed to be a viral response to antiviral treatment and host immune pressure. Sanger sequencing was previously the classic approach for quasispecies analysis, but this method was also time-consuming and laborious. Ultra-deep sequencing has been widely used in viral quasispecies research, especially for low-frequency mutation detection. Here we present a multiple samples deep sequencing method employing the Illumina platform to detect HBV quasispecies variation in patient-derived samples.

A deep sequencing reveals significant diversity among dominant variants and evolutionary dynamics of avian leukosis viruses in two infectious ecosystems

Background

As a typical retrovirus, the evolution of Avian leukosis virus subgroup J (ALV-J) in different infectious ecosystems is not characterized, what we know is there are a cloud of diverse variants, namely quasispecies with considerable genetic diversity. This study is to explore the selection of infectious ecosystems on dominant variants and their evolutionary dynamics of ALV-J between DF1 cells and specific-pathogen-free (SPF) chickens. High-throughput sequencing platforms provide an approach for detecting quasispecies diversity more fully.

Results

An average of about 20,000 valid reads were obtained from two variable regions of gp85 gene and LTR-U3 region from each sample in different infectious ecosystems. The top 10 dominant variants among ALV-J from chicken plasmas, DF1 cells and liver tumor were completely different from each other. Also there was a difference of shannon entropy and global selection pressure values (ω) in different infectious ecosystems. In the plasmas of two chickens, a large portion of quasispecies contained a 3-peptides “LSD” repeat insertion that was only less than 0.01% in DF1 cell culture supernatants. In parallel studies, the LTR-U3 region of ALV-J from the chicken plasmas demonstrated more variants with mutations in their transcription regulatory elements than those from DF1 cells.

Conclusions

Our data taken together suggest that the molecular epidemiology based on isolated ALV-J in cell culture may not represent the true evolution of virus in chicken flocks in the field. The biological significance of the “LSD” insert and mutations in LTR-U3 needs to be further studied.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0902-6) contains supplementary material, which is available to authorized users.

Current molecular methods for the detection of hepatitis B virus quasispecies

Chronic HBV infection affects more than 240 million people worldwide and is associated with a broad range of clinical manifestations including liver cirrhosis, liver failure and hepatocellular carcinoma. Because of the lack of an efficient cure for chronic hepatitis B, the main goal of antiviral therapy is the prevention of liver disease progression coupled with prolonged survival of patients. Because HBV viral load has been shown to be a crucial determinant of the progression of liver damage, these goals can be achieved as long as HBV replication can be suppressed. Unfortunately, long-term therapy with the low-to-moderate genetic barrier drugs, which are still recommended in a majority of developing countries, are strongly associated with HBV resistance development and treatment failure. In such cases, the precise and accurate determination of drug-resistant variants in an individual patient before treatment is important for a proper choice of first-line potent therapy. Nowadays, a number of techniques are available to study HBV quasispecies evolution. This review describes the advantages and limitations of various assays detecting drug-resistant HBV variants. Copyright © 2016 John Wiley & Sons, Ltd.

Analysis of Quasispecies of Avain Leukosis Virus Subgroup J Using Sanger and High-throughput Sequencing

Background

Avian leukosis viruses subgroup J (ALV-J) exists as a complex mixture of different, but closely related genomes named quasispecies subjected to continuous change according to the Principles of Darwinian evolution.

Method

The present study seeks to compare conventional Sanger sequencing with deep sequencing using MiSeq platform to study quasispecies dynamics of ALV-J.

Results

The accuracy and reproducibility of MiSeq sequencing was determined better than Sanger sequencing by running each experiment in duplicate. According to the mutational rate of single position and the ability to distinguish dominant quasispecies with two sequencing methods, conventional Sanger sequencing technique displayed high randomness due to few sequencing samples, while deep sequencing could reflect the composition of the quasispecies more accurately. In the mean time, the research of quasispecies via Sanger sequencing was simulated and analyzed with the aid of re-sampling strategy with replacement for 1000 times repeat from high-throughput sequencing data, which indicated that the higher antibody titer, the higher sequence entropy, the harder analyzing with the conventional Sanger sequencing, resulted in lower ratios of dominant variants.

Conclusions

In sum, deep sequencing is better suited for detecting rare variants comprehensively. The simulation of Sanger sequencing that we propose here will also help to standardize quasispecies researching under different selection pressure based on next-generation sequencing data.

Interaction of Virus Populations with Their Hosts

Viral population numbers are extremely large compared with those of their host species. Population bottlenecks are frequent during the life cycle of viruses and can reduce viral populations transiently to very few individuals. Viruses have to confront several types of constraints that can be divided in basal, cell-dependent, and organism-dependent constraints. Viruses overcome them exploiting a number of molecular mechanisms, with an important contribution of population numbers and genome variation. The adaptive potential of viruses is reflected in modifications of cell tropism and host range, escape to components of the host immune response, and capacity to alternate among different host species, among other phenotypic changes. Despite a fitness cost of most mutations required to overcome a selective constraint, viruses can find evolutionary pathways that ensure their survival in equilibrium with their hosts.

Evidence of an Exponential Decay Pattern of the Hepatitis Delta Virus Evolution Rate and Fluctuations in Quasispecies Complexity in Long-Term Studies of Chronic Delta Infection

Chronic HDV infection can cause a severe form of viral hepatitis for which there is no specific treatment. Characterization of the hepatitis B or C viral quasispecies has provided insight into treatment failure and disease recurrence following liver transplantation, has proven useful to understand hepatitis B e antigen seroconversion, and has helped to predict whether hepatitis C infection will resolve or become chronic. It is likely that characterization of the hepatitis delta virus (HDV) quasispecies will ultimately have similar value for the management of this infection. This study sought to determine the RNA evolution rates in serum of chronic hepatitis delta (CHD) treatment-naïve patients, using next-generation sequencing methods. The region selected for study encompassed nucleotide positions 910 to 1270 of the genome and included the amber/W codon. Amber/W is a substrate of the editing process by the ADAR1 host enzyme and is essential for encoding the 2 delta antigens (HDAg). The amber codon encodes the small (unedited) HDAg form and the W codon the large (edited) HDAg form. The evolution rate was analyzed taking into account the time elapsed between samples, the percentage of unedited and edited genomes, and the complexity of the viral population. The longitudinal studies included 29 sequential samples from CHD patients followed up for a mean of 11.5 years. In total, 121,116 sequences were analyzed. The HDV evolution rate ranged from 9.5x10-3 to 1.2x10-3 substitutions/site/year and showed a negative correlation with the time elapsed between samples (p<0.05). An accumulation of transition-type changes was found to be responsible for higher evolution rates. The percentages of unedited and edited genomes and the quasispecies complexity showed no relationships with the evolution rate, but the fluctuations in the percentages of genomes and in complexity suggest continuous adaptation of HDV to the host conditions.

Hepatitis B virus quasispecies evolution after liver transplantation in patients under long-term lamivudine prophylaxis with or without hepatitis B immune globulin

AIMS

To investigate an optimal long-term prophylactic strategy for prevention of hepatitis B virus (HBV) recurrence after liver transplantation, we conducted a randomized study of 29 transplant recipients receiving a short course of hepatitis B immune globulin (HBIg) + lamivudine (LAM), followed by randomization to long-term prophylaxis with LAM with or without HBIg.

METHODS

The efficacy and safety, and impact on survival and HBV recurrence of these 2 prophylactic regimens were compared over a mean period of 10 years. In patients with viral recurrence, the HBV quasispecies in the surface/polymerase region were studied by ultra-deep pyrosequencing (UDPS).

RESULTS

The 10-year survival rate was 76% and was not affected by the type of prophylaxis. Four patients had hepatitis B surface antigen (HBsAg) recurrence within the first 48 months after orthotopic liver transplantation (OLT). HBsAg-positive and -negative patients showed similar mean survival times, with no differences between the 2 regimens. Low HBV DNA levels were transiently detected in 32% of HBsAg-negative patients. UDPS showed major changes after OLT in the HBV quasispecies of patients with viral recurrence, which may be explained by a "bottleneck" effect of OLT together with prophylactic therapy.

CONCLUSION

Long-term survival after OLT in end-stage chronic hepatitis B patients was good with both prophylactic strategies. However, low, transient HBV DNA levels were detected even in the absence of HBsAg, showing the importance of continuing HBV prophylaxis.

Variability in long-term hepatitis B virus dynamics under antiviral therapy

Hepatitis B virus (HBV) dynamics in treated patients can be complex and differ considerably from other viral infections. We analyse dynamics of liver and serum levels of HBV DNA in 24 chronically HBV-infected individuals undergoing 1 year of combination therapy with pegylated interferon alpha and adefovir dipivoxil (ADV), followed by 2 years of ADV monotherapy. Serum viral dynamics differentiated the patients into four response groups dependent on how quickly viremia became undetectable: quickly suppressed (HBV DNA <100 copies/ml within 8 weeks and staying suppressed, GRP1); quickly suppressed but some rebound (<10,000 copies/ml, GRP2); slow decay (GRP3); virological failures (>10,000 copies/ml, GRP4). These groups did not differ before start of therapy by serum HBV DNA (p=0.2), HBsAg (p=0.1), ALT (p=0.4), total HBV DNA within the liver (p=0.08), or cccDNA (p=0.3). Despite very different serum HBV DNA levels after 3 years, there was no statistical difference in total HBV DNA within the liver (p=0.08), nor in cccDNA levels (p=0.1), but HBsAg levels in serum were significantly lower for GRP1 compared to GRP4 (p=0.02). Efficacy in terms of reduction over the 3 years of serum HBV DNA, liver HBV DNA, cccDNA, and ratios of liver HBV DNA to cccDNA were 99.98%, 99.5%, 98.4%, and 83.2% respectively, exhibiting larger antiviral effects in serum than in liver. Over the course of therapy, HBV DNA viremia exhibited large oscillations for some individuals. Mathematical modelling reproduced the dynamics of these diverse groups by assuming a number of viral clones arose that experienced delayed recognition by the antibody response. Large viremia oscillations under therapy suggest sequential outgrowth of viral clones with delayed recognition by the humoral response.

Composition and Interactions of Hepatitis B Virus Quasispecies Defined the Virological Response During Telbivudine Therapy

Reverse transcriptase (RT) mutations contribute to hepatitis B virus resistance during antiviral therapy with nucleos(t)ide analogs. However, the composition of the RT quasispecies and their interactions during antiviral treatment have not yet been thoroughly defined. In this report, 10 patients from each of 3 different virological response groups, i.e., complete virological response, partial virological response and virological breakthrough, were selected from a multicenter trial of Telbivudine treatment. Variations in the drug resistance-related critical RT regions in 107 serial serum samples from the 30 patients were examined by ultra-deep sequencing. A total of 496,577 sequence reads were obtained, with an average sequencing coverage of 4,641X per sample. The phylogenies of the quasispecies revealed the independent origins of two critical quasispecies, i.e., the rtA181T and rtM204I mutants. Data analyses and theoretical modeling showed a cooperative-competitive interplay among the quasispecies. In particular, rtM204I mutants compete against other quasispecies, which eventually leads to virological breakthrough. However, in the absence of rtM204I mutants, synergistic growth of the drug-resistant rtA181T mutants with the wild-type quasispecies could drive the composition of the viral population into a state of partial virological response. Furthermore, we demonstrated that the frequency of drug-resistant mutations in the early phase of treatment is important for predicting the virological response to antiviral therapy.

Implementation of Next-Generation Sequencing for Hepatitis B Virus Resistance Testing and Genotyping in a Clinical Microbiology Laboratory

Sanger sequencing or DNA hybridization have been the primary modalities for hepatitis B (HBV) resistance testing and genotyping; however, there are limitations, such as low sensitivity and the inability to detect novel mutations. Next-generation sequencing (NGS) for HBV can overcome these limitations, but there is limited guidance for clinical microbiology laboratories to validate this novel technology. In this study, we describe an approach to implementing deep pyrosequencing for HBV resistance testing and genotyping in a clinical virology laboratory. A nested PCR targeting the pol region of HBV (codons 143 to 281) was developed, and the PCR product was sequenced by the 454 Junior (Roche). Interpretation was performed by ABL TherapyEdge based on European Association for the Study of the Liver (EASL) guidelines. Previously characterized HBV samples by INNO-LiPA (LiPA) were compared to NGS with discordant results arbitrated by Sanger sequencing. Genotyping of 105 distinct samples revealed a concordance of 95.2% (100/105), with Sanger sequencing confirming the NGS result. Resistance testing by NGS was concordant with LiPA in 85% (68/80) of previously characterized samples. Additional mutations were found in 8 samples, which related to the identification of low-level mutant subpopulations present at <10% (6/8). To balance the costs of testing for the validation study, reproducibility of the NGS was investigated through an analysis of sequence variants at loci not associated with resistance in a single patient sample. Our validation approach attempts to balance costs with efficient data acquisition.

A novel baseline hepatitis B virus sequencing-based strategy for predicting adefovir antiviral response

Adefovir dipivoxil (ADV) is used as first-line monotherapy or rescue therapy in chronic hepatitis B (CHB) patients. In this study, we sought to identify nucleotide changes in the reverse transcriptase (RT) of hepatitis B virus (HBV) at baseline and explore their predictive value for ADV antiviral response. Ultra-deep pyrosequencing (UDPS) was utilized to determine HBV genetic variability within the RT region at baseline and during a 48-week ADV therapy. According to the viral load at the end of ADV treatment, all patients were classified into responders (HBV DNA level reduction of ⩾ 3 log 10 IU/mL) and suboptimal responders (HBV DNA level reduction of <3 log 10 IU/mL). Based on UDPS data at baseline, we identified 11 nucleotide substitutions whose combination frequency was significantly associated with the antiviral response among 36 CHB patients in the study group. However, the baseline distribution and frequency of rt181 and rt236 substitutions known to confer ADV resistance was a poor predictor for the antiviral response. Compared with baseline serum HBeAg, HBV-DNA and ALT levels, the baseline HBV sequence-based model showed higher predictive accuracy for ADV response. In an independent cohort of 31 validation patients with CHB, the sequence-based model provided greater predictive potency than the HBeAg/HBV-DNA/ALT and the HBeAg/HBV-DNA/ALT/sequence combinations. Taken together, we confirm the presence of ADV resistance variants in treatment-naïve patients and firstly unravel the predictive value of the baseline mutations in the HBV RT region for ADV antiviral response.

Performance assessment of the Illumina massively parallel sequencing platform for deep sequencing analysis of viral minority variants

Massively parallel sequencing (MPS) technology has opened new avenues to study viral dynamics and treatment-induced resistance mechanisms of infections such as human immunodeficiency virus (HIV) and hepatitis C virus (HCV). Whereas the Roche/454 platform has been used widely for the detection of low-frequent drug resistant variants, more recently developed short-read MPS technologies have the advantage of delivering a higher sequencing depth at a lower cost per sequenced base. This study assesses the performance characteristics of Illumina MPS technology for the characterization of genetic variability in viral populations by deep sequencing. The reported results from MPS experiments comprising HIV and HCV plasmids demonstrate that a 0.5-1% lower limit of detection can be achieved readily with Illumina MPS while retaining good accuracy also at low frequencies. Deep sequencing of a set of clinical samples (12 HIV and 9 HCV patients), designed at a similar budget for both MPS platforms, reveals a comparable lower limit of detection for Illumina and Roche/454. Finally, this study shows the possibility to apply Illumina's paired-end sequencing as a strategy to assess linkage between different mutations identified in individual viral subspecies. These results support the use of Illumina as another MPS platform of choice for deep sequencing of viral minority species.

Advanced molecular surveillance of hepatitis C virus

Hepatitis C virus (HCV) infection is an important public health problem worldwide. HCV exploits complex molecular mechanisms, which result in a high degree of intrahost genetic heterogeneity. This high degree of variability represents a challenge for the accurate establishment of genetic relatedness between cases and complicates the identification of sources of infection. Tracking HCV infections is crucial for the elucidation of routes of transmission in a variety of settings. Therefore, implementation of HCV advanced molecular surveillance (AMS) is essential for disease control. Accounting for virulence is also important for HCV AMS and both viral and host factors contribute to the disease outcome. Therefore, HCV AMS requires the incorporation of host factors as an integral component of the algorithms used to monitor disease occurrence. Importantly, implementation of comprehensive global databases and data mining are also needed for the proper study of the mechanisms responsible for HCV transmission. Here, we review molecular aspects associated with HCV transmission, as well as the most recent technological advances used for virus and host characterization. Additionally, the cornerstone discoveries that have defined the pathway for viral characterization are presented and the importance of implementing advanced HCV molecular surveillance is highlighted.

Different mechanism of selection of adefovir-resistant mutant viruses during adefovir monotherapy in patients with lamivudine-resistant chronic hepatitis B

BACKGROUND

Adefovir (ADV) resistance is more frequent in lamivudine (LMV)-resistant chronic hepatitis B (CHB) patients than in nucleos(t)ide analogue-naïve patients. The majority of LMV-resistant mutants harbor the rtM204V/I mutation, while a minor fraction harbor the rtA181V/T mutation. We aimed to elucidate the mechanism of the high rate of ADV resistance in LMV-resistant patients during ADV therapy.

METHODS

We performed a clonal analysis of HBV reverse transcriptase in treatment-naïve (n = 3) and LMV-resistant patients before ADV therapy (n = 14). Dynamic changes in the viral population (n = 9) during ADV therapy were also analyzed.

RESULTS

Before ADV therapy, rtA181V/T was observed in 30 of 680 clones (4.4%) from 7 patients with LMV resistance under dominant rt204V/I mutation and in one of 150 clones in treatment-naïve patients. The rtA181V/T mutation was more frequently found in clones from LMV-resistant patients than in treatment-naïve patients (p = 0.029). The rtN236T mutation was not observed in any clone. During ADV therapy, most rtM204V/I mutants were replaced by wild type in all 3 patients without the rtA181V/T mutation and in one patient with the rtA181V/T mutation. Subsequently, wild type was replaced by the rtN236T and/or rtA181V/T mutant. In patients with the rtA181V/T mutation (n = 6), the rtA181V/T mutant overtook the rtM204V/I mutant in 3 of 4 patients with ADV resistance. In 2 patients without ADV resistance, most of the viral population was replaced by wild type by the last follow-up.

CONCLUSION

The high rate of ADV resistance in patients with LMV-resistance might be attributable to preexisting rtA181V/T mutant virus.

Extensive recombination due to heteroduplexes generates large amounts of artificial gene fragments during PCR

Artificial recombinants can be generated during PCR when more than two genetically distinct templates coexist in a single PCR reaction. These recombinant amplicons can lead to the false interpretation of genetic diversity and incorrect identification of biological phenotypes that do not exist in vivo. We investigated how recombination between 2 or 35 genetically distinct HIV-1 genomes was affected by different PCR conditions using the parallel allele-specific sequencing (PASS) assay and the next generation sequencing method. In a standard PCR condition, about 40% of amplicons in a PCR reaction were recombinants. The high recombination frequency could be significantly reduced if the number of amplicons in a PCR reaction was below a threshold of 10¹³–10¹⁴ using low thermal cycles, fewer input templates, and longer extension time. Heteroduplexes (each DNA strand from a distinct template) were present at a large proportion in the PCR products when more thermal cycles, more templates, and shorter extension time were used. Importantly, the majority of recombinants were identified in heteroduplexes, indicating that the recombinants were mainly generated through heteroduplexes. Since prematurely terminated extension fragments can form heteroduplexes by annealing to different templates during PCR amplification, recombination has a better chance to occur with samples containing different genomes when the number of amplicons accumulate over the threshold. New technologies are warranted to accurately characterize complex quasispecies gene populations.

Investigation into drug-resistant mutations of HBV from 845 nucleoside/nucleotide analogue-naive Chinese patients with chronic HBV infection

BACKGROUND

This study aimed to clarify the clinical significance of drug-resistant HBV in nucleoside/nucleotide analogue (NA)-naive Chinese patients with chronic HBV infection in real clinical practice.

METHODS

A total of 845 NA-naive patients who were admitted to Beijing 302 Hospital between July 2007 and March 2012 were included in the study. HBV drug-resistant mutations were examined by direct sequencing of the viral reverse transcriptase gene and verified by clonal sequencing. Phenotypic analysis of viral replication capacity and drug susceptibility were performed by measuring viral replicative intermediate level in 1.1-mer mutant or wild-type HBV amplicon-transfected HepG2 cells in absence or presence of serially diluted drugs.

RESULTS

Drug-resistant mutations were detected in 2.01% (17/845) of the patients by direct sequencing, including 15 with lamivudine-resistant mutations (rtM204V, rtM204I), one with adefovir-resistant mutation (rtA181V), and one with both lamivudine- and adefovir-resistant mutations (rtA181V, rtM204I). Clonal sequencing identified 13 drug-resistant HBV strains: rtL80I+M204I, rtL80I+M204V, rtL180M+M204I, rtL180M+M204V, rtM204I, rtM204V, rtL80I+L180M+M204I, rtL80I+L180M+M204V, rtA181V, rtA181V+M204I, rtA181T+N236T, rtA181V+N236T and rtN236T. Phenotypic analysis showed that two pre-existing lamivudine-resistant strains (rtL80I+M204I, rtL180M+M204V) had >1,000-fold resistance to lamivudine, and one pre-existing adefovir-resistant strain (rtA181V+N236T) had 15.4-fold resistance to adefovir compared with the wild-type strain. A follow-up study showed that the presence of pre-existing rtM204I strain in one patient increased from 20% at baseline to 85% after 13 months of entecavir treatment with corresponding recession of wild-type strain in the viral pool.

CONCLUSIONS

The incidence of drug-resistant HBV mutations was low in NA-naive Chinese HBV-infected patients. Pre-existing mutants had similar resistance characteristics to those from NA refractory patients.

Prevalence of WHO transmitted drug resistance mutations by deep sequencing in antiretroviral-naïve subjects in Hunan Province, China

BACKGROUND

There are few data on the prevalence of WHO transmitted drug resistance mutations (TDRs) that could affect treatment responses to first line antiretroviral therapy (ART) in Hunan Province, China.

OBJECTIVE

Determine the prevalence of WHO NRTI/NNRTI/PI TDRs in ART-naïve subjects in Hunan Province by deep sequencing.

METHODS

ART-naïve subjects diagnosed in Hunan between 2010-2011 were evaluated by deep sequencing for low-frequency HIV variants possessing WHO TDRs to 1% levels. Mutations were scored using the HIVdb.stanford.edu algorithm to infer drug susceptibility.

RESULTS

Deep sequencing was performed on samples from 90 ART-naïve subjects; 83.3% were AE subtype. All subjects had advanced disease (average CD4 count 134 cells/mm3). Overall 25.6%(23/90) of subjects had HIV with major WHO NRTI/NNRTI TDRs by deep sequencing at a variant frequency level ≥ 1%; 16.7%(15/90) had NRTI TDR and 12.2%(11/90) had a major NNRTI TDR. The majority of NRTI/NNRTI mutations were identified at variant levels <5%. Mutations were analyzed by HIVdb.stanford.edu and 7.8% of subjects had variants with high-level nevirapine resistance; 4.4% had high-level NRTI resistance. Deep sequencing identified 24(27.6%) subjects with variants possessing either a PI TDR or hivdb.stanford.edu PI mutation (algorithm value ≥ 15). 17(19.5%) had PI TDRs at levels >1%.

CONCLUSIONS

ART-naïve subjects from Hunan Province China infected predominantly with subtype AE frequently possessed HIV variants with WHO NRTI/NNRTI TDRs by deep sequencing that would affect the first line ART used in the region. Specific mutations conferring nevirapine high-level resistance were identified in 7.8% of subjects. The majority of TDRs detected were at variant levels <5% likely due to subjects having advanced chronic disease at the time of testing. PI TDRs were identified frequently, but were found in isolation and at low variant frequency. As PI/r use is infrequent in Hunan, the existence of PI mutations likely represent AE subtype natural polymorphism at low variant level frequency.

Pre-S mutations of hepatitis B virus affect genome replication and expression of surface antigens

BACKGROUNDS AND AIMS

In chronic hepatitis B virus (HBV) infection, quantitative HBV surface antigen (qHBsAg) is useful for monitoring viral replication and treatment responses. We aimed to determine whether pre-S mutations have any effect on circulating qHBsAg.

METHODS

Plasmids expressing 1–8 amino acid deletion in pre-S1 ("pre-S1Δ1-8") and 3-25 amino acid deletion in pre-S2 ("pre-S2Δ3-25") were constructed. At 72 h posttransfection into Huh7 cells, qHBsAg were measured using electrochemiluminescence immunoassay analyzer. To mimic milieus of quasispecies, we co-transfected either pre-S1Δ1-8 or pre-S2Δ3-25 with wild type (WT).

RESULTS

Pre-S mutations affected transcription and replication ability of HBV because of altered overlapping polymerase. Compared with WT, extracellular qHBsAg in pre-S1Δ1-8 and pre-S2Δ3-25 were on average 3.87-fold higher and 0.92-fold lower, respectively, whereas intracellular qHBsAg in pre-S1Δ1-8 and pre-S2Δ3-25 were 0.57-fold lower and 1.60-fold higher, respectively. Immunofluorescence staining of cellular HBsAg showed that pre-S1Δ1-8 had less staining and that pre-S2Δ3-25 had denser staining. As ratios of either pre-S1Δ1-8 or pre-S2Δ3-25:WT increased from 0:10 to 10:0 gradually, relative extracellular qHBsAg increased from 1.0 to 3.85 in pre-S1Δ1-8 co-transfection, whereas those decreased from 1.0 to 0.88 in pre-S2Δ3-25 co-transfection.

CONCLUSION

Pre-S mutations exhibit different phenotypes of genome replication and HBsAg expression according to their locations. Thus, qHBsAg level for diagnosis and prognostification in chronic HBV infection should be used more cautiously, considering emergences of pre-S deletion mutants.

rtM204Q may serve as a novel lamivudine-resistance-associated mutation of hepatitis B virus

Background and Aims

Lamivudine (LAM) is still widely used for anti-HBV therapy in China. The study aimed to clarify whether a newly-found rtM204Q mutation from patients was associated with the drug resistance.

Methods

HBV complete reverse-transcriptase region was screened by direct sequencing and verified by clonal sequencing. Replication-competent plasmids containing patient-derived 1.1mer mutant or wild-type viral genome were constructed and transfected into HepG2 cells. After cultured with or without serially-diluted antiviral drugs, intracellular HBV replicative intermediates were quantitated for calculating the 50% effective concentration of drug (EC₅₀).

Results

A total of 12,000 serum samples of 9,830 patients with chronic HBV infection were screened. rtM204Q mutation was detected in seven LAM-refractory patients. By contrast, rtM204I/rtM204V mutations were detected in 2,502 patients' samples. The rtM204Q emerged either alone or in concomitance with rtM204I/rtM204V, and all were accompanied with virologic breakthrough in clinical course. Clonal sequencing verified that rtM204Q mutant was predominant in viral quasispecies of these samples. Phenotypic analysis showed that rtM204Q mutant had 89.9% of replication capacity and 76-fold increased LAM EC₅₀ of the concomitant wild-type strain. By contrast, rtM204I mutant in the sample had lower replication capacity and higher LAM resistance (46.3% and 1396-fold increased LAM EC₅₀ of the wild-type strain) compared to rtM204Q mutant. rtM204Q mutant was susceptible to adefovir dipivoxil (ADV) in vitro and ADV/ADV+LAM rescue therapy in clinic.

Conclusion

rtM204Q is suggested to be a novel LAM-resistance-associated mutation. It conferred a moderate resistance with higher competent natural replication capacity compared to rtM204I mutation.

Application of deep sequence technology in hepatology

Deep sequencing technologies are currently cutting edge, and are opening fascinating opportunities in biomedicine, producing over 100-times more data compared to the conventional capillary sequencers based on the Sanger method. Next-generation sequencing (NGS) is now generally defined as the sequencing technology that, by employing parallel sequencing processes, producing thousands or millions of sequence reads simultaneously. Since the GS20 was released as the first NGS sequencer on the market by 454 Life Sciences, the competition in the development of the new sequencers has become intense. In this review, we describe the current deep sequencing systems and discuss the application of advanced technologies in the field of hepatology.

Clinical application of estimating hepatitis B virus quasispecies complexity by massive sequencing: correlation between natural evolution and on-treatment evolution

AIM

To evaluate HBV quasispecies (QA) complexity in the preCore/Core regions in relation to HBeAg status, and explore QA changes under natural evolution and nucleoside analogue (NUC) treatment.

METHODS

Ultra-deep pyrosequencing of HBV preCore/Core regions in 30 sequential samples (baseline [diagnosis], treatment-free, and treatment-nonresponse) from 10 retrospectively selected patients grouped according to HBeAg status over time: HBeAg+ (N = 4), HBeAg- (N = 2), and fluctuating HBeAg (transient seroreversion/seroconversion pattern) (N = 4). QA complexity was defined by Shannon entropy, mutation frequency, nucleotide diversity, and mutation frequency of amino acids (MfAA) in preCore and Core.

RESULTS

The QA was less complex in HBeAg+ than in HBeAg- or fluctuating HBeAg. High complexity in preCore was associated with decreased viral replication (preCore MfAA negatively correlated with HBV-DNA, p = 0.005). QA complexity in the treatment-free period negatively correlated with values seen during treatment. Specific variants were mainly selected in the Core region in HBeAg- and fluctuating HBeAg patients, suggesting higher immune pressure than in HBeAg+.

CONCLUSIONS

The negative correlation between QA natural evolution and on-treatment evolution indicates the importance of pre-treatment QA study to predict QA changes in NUC nonresponders. Study of QA complexity could be useful for managing HBV infection.

Comparison of next-generation sequencing and clone-based sequencing in analysis of hepatitis B virus reverse transcriptase quasispecies heterogeneity

We previously reported that, based on clone-based sequencing (CBS), hepatitis B virus (HBV) heterogeneity within the reverse transcriptase (RT) region was a predictor of antiviral efficacy. Here, by comparing ultradeep pyrosequencing (UDPS), i.e., next-generation sequencing (NGS), with CBS in characterizing the genetic heterogeneity of HBV quasispecies within the RT region, we evaluated the performance of UDPS in the analysis of HBV viral populations. HBV genomic DNA was extracted from serum samples from 31 antiviral treatment-naive patients with chronic hepatitis B. The RT region quasispecies were analyzed in parallel using CBS and UDPS. Characterization of quasispecies heterogeneity was conducted using bioinformatics analysis. Quasispecies complexity values were calculated with the formula Sn = -Σi(pilnpi)/lnN. The number of qualified strains obtained by UDPS was much larger than that obtained by CBS (P < 0.001). Pearson analysis showed that there was a positive correlation of quasispecies complexity values at the nucleotide level for the two methods (P < 0.05), while the complexity value derived from UDPS data was higher than that derived from CBS data (P < 0.001). Study of the prevalences of variations within the RT region showed that CBS detected an average of 9.7 ± 1.1 amino acid substitutions/sample and UDPS detected an average of 16.2 ± 1.4 amino acid substitutions/sample. The phylogenetic analysis based on UDPS data showed more genetic entities than did that based on CBS data. Viral heterogeneity determination by the UDPS technique is more sensitive and efficient in terms of low-abundance variation detection and quasispecies simulation than that by the CBS method, although imperfect, and thus sheds light on the future clinical application of NGS in HBV quasispecies studies.

Quasispecies structure, cornerstone of hepatitis B virus infection: Mass sequencing approach

Hepatitis B virus (HBV) is a DNA virus with complex replication, and high replication and mutation rates, leading to a heterogeneous viral population. The population is comprised of genomes that are closely related, but not identical; hence, HBV is considered a viral quasispecies. Quasispecies variability may be somewhat limited by the high degree of overlapping between the HBV coding regions, which is especially important in the P and S gene overlapping regions, but is less significant in the X and preCore/Core genes. Despite this restriction, several clinically and pathologically relevant variants have been characterized along the viral genome. Next-generation sequencing (NGS) approaches enable high-throughput analysis of thousands of clonally amplified regions and are powerful tools for characterizing genetic diversity in viral strains. In the present review, we update the information regarding HBV variability and present a summary of the various NGS approaches available for research in this virus. In addition, we provide an analysis of the clinical implications of HBV variants and their study by NGS.

Characterization of the dynamics of hepatitis B virus resistance to adefovir by ultra-deep pyrosequencing

Hepatitis B virus (HBV) resistance to nucleoside/nucleotide analogs is frequent. Ultra-deep pyrosequencing (UDPS) is a powerful new tool that can detect minor viral variants and characterize complex quasispecies mixtures. We used UDPS to analyze the dynamics of adefovir-resistant HBV variants in patients with chronic HBV infection in whom adefovir resistance occurred during treatment. Amino acid substitutions known to confer resistance to adefovir were detected at baseline in most patients. The dynamics of adefovir-resistant variants were complex and differed among patients as a result of evolving differences in variant fitness. UDPS analysis revealed successive waves of selection of HBV populations with single and multiple amino acid substitutions. Adefovir-resistant variants were partially inhibited by lamivudine, but remained fit in its presence.

CONCLUSION

Substitutions conferring HBV resistance to nucleoside/nucleotide analogs exist before treatment, and that the dynamics of adefovir-resistant populations are much more complex and heterogeneous than previously thought and involve thus far unknown amino acid substitutions. The UDPS-based approach described here is likely to have important implications for the assessment of antiviral drug resistance in research and clinical practice.

Association of preexisting drug-resistance mutations and treatment failure in hepatitis B patients

The role of preexisting minority drug-resistance mutations in treatment failure has not been fully understood in chronic hepatitis B patients. To understand mechanisms of drug resistance, we analyzed drug-resistance mutations in 46 treatment-failure patients and in 29 treatment-naïve patients and determined linkage patterns of the drug-resistance mutations in individual viral genomes using a highly sensitive parallel allele-specific sequencing (PASS) method. Lamivudine resistance (LAMr) mutations were predominant in treatment-failure patients, irrespective of the inclusion of LAM in the regimen. The primary LAMr mutations M204V and M204I were detected in 100% and 30% of the treatment-failure patients, respectively. Two secondary LAMr mutations (L180M and V173L) were also found in most treatment-failure patients (87% and 78%, respectively). The linkages containing these three mutations dominated the resistant viruses. Importantly, minority LAMr mutations present in <2% of the viral population were detected in 83% of the treatment-naïve patients. Moreover, the low-frequency same linked LAMr mutations (<0.15%) were detected in 24% of the treatment-naïve patients. Our results demonstrate that the selection of preexisting minority linked LAMr mutations may be an important mechanism for the rapid development of LAM resistance, caution the continuous use of LAM to treat drug-experienced and -naïve hepatitis B patients, and underline the importance of the detection of minority single and linked drug-resistance mutations before initiating antiviral therapy.

Ultrasensitive amplification refractory mutation system real-time PCR (ARMS RT-PCR) assay for detection of minority hepatitis B virus-resistant strains in the era of personalized medicine

Resistance to antiviral treatment for chronic hepatitis B virus (HBV) has been associated with mutations in the HBV polymerase region. This study aimed at developing an ultrasensitive method for quantifying viral populations with all major HBV resistance-associated mutations, combining the amplification refractory mutation system real-time PCR (ARMS RT-PCR) with a molecular beacon using a LightCycler. The discriminatory ability of this method, the ARMS RT-PCR with molecular beacon assay, was 0.01 to 0.25% for the different HBV resistance-associated mutations, as determined by laboratory-synthesized wild-type (WT) and mutant (Mut) target sequences. The assay showed 100% sensitivity for the detection of mutant variants A181V, T184A, and N236T in samples from 41 chronically HBV-infected patients under antiviral therapy who had developed resistance-associated mutations detected by direct PCR Sanger sequencing. The ratio of mutant to wild-type viral populations (the Mut/WT ratio) was >1% in 38 (63.3%) of 60 samples from chronically HBV-infected nucleos(t)ide analogue-naive patients; combinations of mutations were also detected in half of these samples. The ARMS RT-PCR with molecular beacon assay achieved high sensitivity and discriminatory ability compared to the gold standard of direct PCR Sanger sequencing in identifying resistant viral populations in chronically HBV-infected patients receiving antiviral therapy. Apart from the dominant clones, other quasispecies were also quantified. In samples from chronically HBV-infected nucleos(t)ide analogue-naive patients, the assay proved to be a useful tool in detecting minor variant populations before the initiation of the treatment. These observations need further evaluation with prospective studies before they can be implemented in daily practice.

A comparative study of ultra-deep pyrosequencing and cloning to quantitatively analyze the viral quasispecies using hepatitis B virus infection as a model

In this study, the reliability and reproducibility of viral quasispecies quantification by three ultra-deep pyrosequencing (UDPS) methods (FLX+, FLX, and Junior) were investigated and results compared with the conventional cloning technique. Hepatitis B virus (HBV) infection was selected as the model. The preCore/Core region, the least overlapped HBV region, was analyzed in samples from a chronic hepatitis B patient by cloning and by UDPS. After computation filtering of the UDPS results, samples A1 and A2 (FLX+) and sample B (FLX) yielded the same 20 polymorphic positions. Junior yielded 18 polymorphic positions that coincided with the FLX results. In contrast, 50 polymorphic positions were detected by cloning. Quasispecies complexity plotted on graphs showed superimposed patterns and the quantitative parameters were similar between FLX+, FLX, Junior, and the cloning sequences. Twenty-two haplotypes were detected by Junior, and 37, 40, and 39 were detected by FLX A1, A2, and B, respectively. These differences may be attributable to methodological differences between FLX and Junior. By cloning, 47 haplotypes were detected. Eight clones with insertions and deletions that induced de novo stop codons were not observed by UDPS because the UDPS filter discarded them. Our results indicate that UDPS is an optimal alternative to molecular cloning for quantitative study of the viral quasispecies. Nonetheless, specific mutations, such as insertions and deletions, were only detected by cloning. A filter should be designed to analyze cloning sequences, and UDPS filters should be improved to include the specific mutations.

Diagnostic and therapeutic progress of multi-drug resistance with anti-HBV nucleos(t)ide analogues

Nucleos(t)ide analogues (NA) are a breakthrough in the treatment and management of chronic hepatitis B. NA could suppress the replication of hepatitis B virus (HBV) and control the progression of the disease. However, drug resistance caused by their long-term use becomes a practical problem, which influences the long-term outcomes in patients. Liver transplantation is the only choice for patients with HBV-related end-stage liver disease. But, the recurrence of HBV after transplantation often caused by the development of drug resistance leads to unfavorable outcomes for the recipients. Recently, the multi-drug resistance (MDR) has become a common issue raised due to the development and clinical application of a variety of NA. This may complicate the antiviral therapy and bring poorly prognostic outcomes. Although clinical evidence has suggested that combination therapy with different NA could effectively reduce the viral load in patients with MDR, the advent of new antiviral agents with high potency and high genetic barrier to resistance brings hope to antiviral therapy. The future of HBV researches relies on how to prevent the MDR occurrence and develop reasonable and effective treatment strategies. This review focuses on the diagnostic and therapeutic progress in MDR caused by the anti-HBV NA and describes some new research progress in this field.

Detection of primary YMDD mutations in HBV-related hepatocellular carcinoma using hybridization-fluorescence polarization

Lamivudine is used for the treatment of hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC). However, HBV-related HCC patients with mutations in the tyrosine-methionine-aspartate-aspartate (YMDD) motif have no response to lamivudine therapy. The detection of YMDD mutations in HBV-related HCC patients may help guide the treatment of HCC. In this study, a simple, sensitive, reliable and cost-effective hybridization-fluorescence polarization assay for the detection of YMDD mutations in HCC was developed. A pair of general primers within the highly conserved region of the HBV polymerase gene was used in an asymmetric PCR. Three probes specific for the corresponding YMDD mutations labeled with different fluorescent reporters hybridized to their target amplicons, and hybridization was indicated by higher fluorescence polarization. The hybridization-fluorescence polarization assay was capable of detecting YMDD mutations at a limit of detection of 10 copies per reaction, and the assay was able to detect minor populations of viruses with primary YMDD mutations as low as 10%. The rates of primary YMDD mutations and the correlation between YMDD mutations and HBV genotypes in 251 HBV-related HCC patients were investigated using the hybridization-fluorescence polarization assay.

Quasispecies dynamics in main core epitopes of hepatitis B virus by ultra-deep-pyrosequencing

AIM: To investigate the variability of the main immunodominant motifs of hepatitis B virus (HBV) core gene by ultra-deep-pyrosequencing (UDPS).

METHODS: Four samples (2 genotype A and 2 genotype D) from 4 treatment-naïve patients were assessed for baseline variability. Two additional samples from one patient (patient 4, genotype D) were selected for analysis: one sample corresponded to a 36-mo treatment-free period from baseline and the other to the time of viral breakthrough after 18 mo of lamivudine treatment. The HBV region analyzed covered amino acids 40 to 95 of the core gene, and included the two main epitopic regions, Th50-69 and B74-84. UDPS was carried out in the Genome Sequencer FLX system (454 Life Sciences, Roche). After computer filtering of UDPS data based on a Poisson statistical model, 122 813 sequences were analyzed. The most conserved position detected by UDPS was analyzed by site-directed mutagenesis and evaluated in cell culture.

RESULTS: Positions with highest variability rates were mainly located in the main core epitopes, confirming their role as immune-stimulating regions. In addition, the distribution of variability showed a relationship with HBV genotype. Patient 1 (genotype A) presented the lowest variability rates and patient 2 (genotype A) had 3 codons with variability higher than 1%. Patient 3 and 4 (both genotype D) presented 5 and 8 codons with variability higher than 1%, respectively. The median baseline frequencies showed that genotype A samples had higher variability in epitopic positions than in the other positions analyzed, approaching significance (P = 0.07, sample 1 and P = 0.05, sample 2). In contrast, there were no significant differences in variability between the epitopic and other positions in genotype D cases. Interestingly, patient 1 presented a completely mutated motif from amino acid 64 to 67 (E₆₄LMT₆₇), which is commonly recognized by T helper cells. Additionally, the variability observed in all 4 patients was particularly associated with the E₆₄LMT₆₇ motif. Codons 78 and 79 were highly conserved in all samples, in keeping with their involvement in the interaction between the HBV virion capsid and the surface antigens (HBsAg). Of note, codon 76 was even more conserved than codons 78 and 79, suggesting a possible role in HBsAg interactions or even in hepatitis B e antigen conformation. Sequential analysis of samples from patient 4 (genotype D) illustrated the dynamism of the HBV quasispecies, with strong selection of one minor baseline variant coinciding with a decrease in core variability during the treatment-free and lamivudine-treated period. The drop in variability seemed to result from a “steady state” situation of the HBV quasispecies after selection of the variant with greatest fitness.

CONCLUSION: Host immune pressure seems to be the main cause of HBV core evolution. UDPS analysis is a useful technique for studying viral quasispecies.

Challenges and opportunities in estimating viral genetic diversity from next-generation sequencing data

Many viruses, including the clinically relevant RNA viruses HIV (human immunodeficiency virus) and HCV (hepatitis C virus), exist in large populations and display high genetic heterogeneity within and between infected hosts. Assessing intra-patient viral genetic diversity is essential for understanding the evolutionary dynamics of viruses, for designing effective vaccines, and for the success of antiviral therapy. Next-generation sequencing (NGS) technologies allow the rapid and cost-effective acquisition of thousands to millions of short DNA sequences from a single sample. However, this approach entails several challenges in experimental design and computational data analysis. Here, we review the entire process of inferring viral diversity from sample collection to computing measures of genetic diversity. We discuss sample preparation, including reverse transcription and amplification, and the effect of experimental conditions on diversity estimates due to in vitro base substitutions, insertions, deletions, and recombination. The use of different NGS platforms and their sequencing error profiles are compared in the context of various applications of diversity estimation, ranging from the detection of single nucleotide variants (SNVs) to the reconstruction of whole-genome haplotypes. We describe the statistical and computational challenges arising from these technical artifacts, and we review existing approaches, including available software, for their solution. Finally, we discuss open problems, and highlight successful biomedical applications and potential future clinical use of NGS to estimate viral diversity.